86 THE VITALITY AND GERMINATION OF SEEDS. 



tested with iodine there was still a deep, purplish-blue color. In this 

 last case the average percentage of germination had decreased to 37.6 

 per cent, as compared with 76.6 per cent for the control samples. 

 Moreover, in the latter case, the onion, phlox, and pansy seeds were 

 killed. 



These results show that there is a remarkable uniformity between 

 the loss in vitality of seeds and the loss in the enzymic action of the 

 "Taka" diastase under similar conditions, but it does not furnish con- 

 clusive evidence that the loss in vitality of the seeds is in any Avay 

 governed by the particular enzymes present. In fact, the evidence at 

 hand better substantiates the opposite view. In the first place dead 

 seeds may still contain active ferments. Secondly, the prolonged sub- 

 jection of seeds to the action of ether and chloroform is generally 

 accompanied by a premature death, and if the seeds are moist the loss 

 in vitality is much more marked. On the other hand, it is generally 

 accepted that either of these gases exerts no injurious effect on the 

 hydroly tic action of the various ferments. Townsend a has shown that 

 the action of diastase on starch paste is even more energetic in the 

 presence than in the absence of ether, but in germination ether usually 

 has a retarding influence. In some cases, however, growth is stimu- 

 lated by the use of ether. 



In the third place enzymes can not be the chief factors controlling 

 the vitality of a seed, because the more sensitive growing point of 

 the radicle suffers injury much in advance of the other portions of 

 the seed. Not infrequently in making germination tests do we find 

 that the growing tip of the embryo is dead, while other portions of 

 the seed may still be living and capable of carrying on all normal met- 

 abolic processes. The bean is one of the best examples for demon- 

 strating this fact. Here the radicle may be entirely dead, yet the 

 cotyledons may still be able to make some growth; but in all seeds 

 where the growing tip is dead the remaining portion of the radicle 

 may be living, in which case adventitious roots may be formed and 

 growth may continue for a considerable time, though very rarely will 

 a healthy seedling be developed. It thus seems quite clear that the real 

 vital elements are closely associated with the growing point, and when 

 this portion of the embryo is once dead the vital energy in the other 

 parts of the seed is not of such a nature as to enable growth to con- 

 tinue for any length of time. Even though the reserve food products 

 are digested they can not be assimilated by the growing radicle, which 

 should be the case were enzymes the chief elements to which the 

 preservation of vitality is attributed. 



Enzymes play an important part in the vitality of seeds, and are 

 undoubtedly necessary for the normal development of a seedling, but 

 the points above given show that the life of a seed is not entirely 



Bot. Gaz., 1899, 27: 458-466. 



